Block polymers have applications in thermoplastic elastomers (TPEs), pressure-sensitive adhesives (PSAs), blend compatibilizers, and devices that require phase-separated nanostructures (e.g., lithographic devices, electronic devices, photovoltaic devices, separation membranes, drug-delivery vehicles, and templates for data storage). Commonly available block polymers are petroleum-based, such as polystyrene-b-poly(methyl methacrylate), polystyrene-b-poly(isoprene), polyether-b-poly(urethane), poly(styrene-b-isoprene-b-styrene) [SIS] and poly(styrene-b-butadiene-b-styrene) [SBS]. The demand for polystyrene (PS) and PS-containing plastics, such as SIS and SBS, was approximately 24 million metric tons in 2011. The production of synthetic and natural rubbers, such as poly(isoprene) [PI], was ˜14.5 million and ˜11.2 million metric tons, respectively, in 2011. However, these petroleum-based polymers require hazardous monomers that should be replaced, including styrene, isoprene, butadiene, methylene diphenyl di-isocyanate, toluene di-isocyanate, and diamines that are volatile organic compounds (VOCs), hazardous air pollutants (HAPs) and/or potentially carcinogenic.
With regard to replacing petroleum-based plastics, U.S. demand for sustainable bio-based plastics is growing at 20% annually, and the turnaround times for commercializing new bio-based plastics can be rapid. For example, the initial push to commercialize poly(lactic acid) (PLA) derived from biomass (primarily from corn starch in the U.S.) began in 1997 and in 2011, approximately 140,000 metric tons of PLA were produced worldwide. Similarly, 170,000 metric tons of corn-based 1,3-propanediol for the synthesis of polytrimethylene terephthalate were produced in 2007 by DuPont Tate & Lyle Bioproducts. Numerous other bio-based plastics and bio-plastics also exist, such as polymenthide, polyhydroxyalkanoates, poly(alpha-methylene-gamma-butyrolactone), and their block polymers. However, the feedstocks for these bio-based plastics (e.g., mint, corn, sugarcane, and/or tulips), and their resulting properties, limit their commercial viability and sometimes their overall sustainability. For instance, implementing edible or presently low-volume feedstocks in commodity applications has the potential impact of reducing global food supply and available land for food production.
As a more sustainable feedstock, lignin is nature's most abundant aromatic chemical and is readily available (more than 70 million metric tons of lignin are harvested annually) as a waste product from the pulp and paper industry. Lignin is capable of yielding valuable low-molecular-weight aromatic chemicals when strategically depolymerized (e.g., vanillin from the sulfite pulping process). These aromatic chemicals may be further functionalized and polymerized. Functionalized lignin-derived molecules and/or functionalized lignin model compounds (which reproduce the lignin-derived molecules' structures and may be petroleum-based) are also referred to as lignin-based monomers. The incorporation of aromaticity in a plastic's chemical structure is known to improve overall plastic performance, such as the aromatic moiety in PS and PS-containing plastics. Thus, a lignin feedstock would require no extra land, deplete no additional resources, and avoid consumption of staple foods in the commodity production of renewable alternatives to PS and other high-performance, aromatic polymers.
In the interest of producing block polymers with rubbery segments for TPEs or PSAs, a monomer source that yields plastics softer than lignin is necessary. Polymerized derivatives of fatty acids and fatty alcohols are known to exhibit low glass transition temperatures (Tg's≈−50° C.) (are soft materials). These fatty-type monomers can be sourced, for example, from used cooking oils (e.g., plant oils), grease, or animal fats. It is estimated that ˜3 million metric tons of used cooking oils (UCO)s and trap grease are generated annually in the U.S. alone. Over 150 million tons/year of vegetable oils are available worldwide. As a high-volume resource, fatty acids and fatty alcohols also may serve as a sustainable feedstock for bio-based block polymers.
Until now, lignin-based monomers and fatty-type monomers have not been block polymerized with each other. Between their aromatic (hard, high Tg) and alkane (soft, low Tg) character in polymerized form, using these renewable monomers as starting materials for the synthesis of block polymers provides a means for creating a wide array of tailorable, high-performance, and widely applicable sustainable plastics, especially TPEs and PSAs.